1. Field of the Invention
The invention relates to a filtering medium and method for filtering solids from organic-based feed streams to chemical reactors. In another aspect, this invention relates to a filtering medium and method for providing flow distribution of organic-based feed streams to chemical reactors. More particularly, the invention relates to a filtering medium and method for filtering solids and providing liquid distribution for organic-based feed streams that are subsequently processed in chemical reactors having discrete solid element catalyst bed(s). A further aspect of the invention relates to a filtering medium and method for partially reacting polymer precursors in organic-based feed streams to chemical reactors to reduce fouling of the solid element catalyst bed(s).
2. Description of Related Art
Typically chemical reactor beds include discrete solid catalyst particles contained in one or more fixed beds. Often these beds are supported, or retained, at their inlet and/or outlet by materials which are inert to the reaction. These inert materials may trap all or some solid contaminants such as dirt, iron oxide, iron sulfide, asphaltenes, coke fines, catalyst fines, sediments or other entrained foreign particulate material in the reactor feed stream. The trapping of the contaminants is to prevent undesirable material from plugging, poisoning or otherwise deactivating the catalyst bed. The inert materials, or inerts, traditionally used are typically made of ceramic material in the form of pellets or spheres and typically must be resistant to crushing, high temperatures and/or high pressures. In addition, these materials may facilitate distribution of the feed stream across the catalyst bed in such a manner to reduce channeling through the catalyst bed.
For the last ten to fifteen years, high void fraction ceramic bed toppings, such as inert ceramic cylindrical filter units with cross sections of approximately ⅜ inch thicknesses and approximately ½ inch to 1¼ inches in diameter with five to ten internal holes of approximately ⅛ inch size, the holes being round or triangular shaped, have been used on the top of fixed bed reactors processing organic feed streams. These bed toppings have been relatively successful at reducing pressure drops by improving liquid distribution. However, attempts to trap particulate matter have not been as successful. Catalyst bed plugging with contaminants such as dirt, iron oxide, iron sulfide, asphaltenes, coke fines, catalyst fines, sediments, or other entrained foreign particulate material remains to be a problem for the industry. Skimming, or removal, of the top portion of the catalyst is required when the filtering capacity of the bed topping or inerts is exhausted resulting in the catalyst itself being used as a filter. Thus, it is highly desirable to increase the efficiency of the inert bed filtration.
In addition to catalyst fouling by particulate matter in the organic-based stream, polymerization of polymer precursors, e.g., diolefins, found in the organic-based feed stream may also foul the catalyst. In particular, two mechanisms of polymerization, free radical polymerization and condensation-type polymerization, may cause catalyst bed fouling, gumming or plugging. The addition of antioxidants to control free radical polymerization has been found useful where the organic-based feed stream has encountered oxygen. Condensation polymerization of diolefins typically occurs after the organic-based feed is heated. Therefore, filtering prior to the organic-based feed stream entering the reactor may not be helpful to remove these foulants as the polymerization reactions generally take place in the reactors.
It is highly desirable to increase the efficiency of the inert bed filtration and to control the rate of reaction of the diolefins or other polymer precursors. Thus, the development of a filtering medium and method for filtration that increases the efficiency of the filtering of the contaminated feed stream may also reduce the pressure drop associated with plugging. The method of the present invention for filtration and flow distribution for chemical reactors, when compared with previously proposed prior art methods, has the advantages of: providing more efficient filtering; increasing catalyst life; decreasing catalyst losses; and reducing the need to take the reactor off-line for maintenance when removal or replacement of the inert material or any catalyst that is plugged is required. These benefits may result in both capital and operating savings.
Disadvantages associated with current filtration and liquid distribution designs and methods in fixed bed chemical reactors may result in poor liquid distribution to the catalyst bed. Partial plugging of the catalyst bed with contaminants, or gumming by reactive diolefins or other polymer precursors, may also cause maldistribution. The maldistribution may result in channeling and corresponding bypassing of portions of the catalyst bed, reducing the catalyst efficiency. Usually, a maldistribution problem is evidenced by radial temperature differences across the reactor. Therefore, the art has sought a medium and method for flow distribution that may spread the liquid more uniformly across and subsequently through the catalyst bed, provide efficient filtering and reduce fouling caused by undesired polymerization reactions.
Accordingly, prior to the development of the present invention, filtering media and methods for filtering, or distributing, organic-based feed streams to chemical reactors had limited abilities to provide both feed distribution and filtering capacity without plugging or blinding. Relatively large pressure drops across the filtering and/or distribution media of the previous apparatus and methods require excessive capital and operating costs and cause process safety and environmental concerns arising from maintenance required shutdowns and start-ups. Therefore, the art has sought a method for extending the run life of catalyst beds by filtering and distributing organic-based feed streams to chemical reactors which does not: require excessive amounts of catalyst; cause relatively large pressure drops across the bed; require relatively large capacity circulation pumps or compressors; and cause process safety and environmental concerns arising from reactor shutdowns and start-ups.